Recently, the demand for tires having high energy efficiency is increasing, and tire manufacturers are continually directing much effort to the development of tires having superior fuel economy to comply with the demand. Furthermore, through research into preventing the fuel economy and wet grip of tires from deteriorating is ongoing. In order to sufficiently exhibit the properties required of tires, rubber for tires must be designed to satisfy the requirements of tires.
To attain the desired properties of tires, modified rubber compositions (e.g. SSBR), resulting from modifying the end of the molecular chain of a modified conjugated diene-based polymer, are being used. The production of such compositions depends on a conventional batch polymerization process, and thus suffers from limited productivity and difficult mixing with silica as a filler for the modified rubber composition.
On the other hand, a continuous polymerization process for the production of synthetic rubber is advantageous because of high production rate and wide molecular weight distribution, thus exhibiting high processability and uniform quality. In modified rubber in which the end of the polymer chain is modified, the efficiency of modification of the end is regarded as important, but the continuous process makes it difficult to obtain high modification efficiency. This is because the growing end of the polymer chain is deactivated due to impurities contained in the continuously fed monomer and solvent.
With the goal of solving this problem, Japanese Patent Application Publication No. 2011-219701 discloses the preparation of a modified conjugated diene polymer using a multifunctional polymerization initiator, but high modification efficiency cannot be obtained in a continuous process, and only a batch polymerization process is described in the embodiments thereof.
Therefore, in the present invention, there is a need for research and development into a modified rubber composition having high modification efficiency and a method of manufacturing the same, in which the use of a multifunctional initiator makes it possible to attain modification efficiency corresponding to that of a batch process, even in a continuous process, and superior properties of the polymer and a desired rubber composition may be obtained.